been handed a wiring diagram for a large heating system, the diagram includes a part labelled  SPDT (and has a electrical symbol type drawing of a couple of components) .  In the print at the bottom is states this part is not included.

What is this part? Anyone installed one? I take it im going to have to make it myself?

Cheers lads

Sounds like a relay.

Why not post the diagram?

Most wholesalers keep the relays, bases and enclosures.

Edmundsons and likely many others keep a budget brand called IMO - They manufacturer the relay, base and enclosures with dinrail.

http://www.imopc.com/products/6/enclosures.html

oppppps forgot to put the numbers on!

Cm - fires boilers up
NC- ORANGE FROM hot water zone valve
NO- PERM LIVE
N- neutral
L- BOTH oranges form both zone vales

Both boilers are meant to fire for heating, one boiler is meant to fire for hot***er, besides this part and the fact theres two shunt pumps both truned on from Cm, i cant see how these boilers will work independently as it looks like a standard S plan with two heating zones????

more i look more i dont understand

cheers so i all i have to get is a SPDT relay and a enclosure?

I cant see how this system is going to work as the plumber wants at all.

to start thankyou very much guys for all the help didnt fire up the system today due to quite a bit of extra work needed and plumber wasnt  ready but did wire a fair bit of the panel including the relay, which thanks to your advice i understood even though it wasnt the correct one as Lec pointed out.  

To save starting a new thread i though i would add to this one.  

My concern now revolves around loading of the system. The supply is from a D16 breaker, then it went into the panel and through B6 breakers.  I have had to remove these breakers to allow for a more traditional system plan.  My problem is these boilers are large and there are four small pumps and one large pump.  Some items such as wireless stats require the supply to be fused to 3amp.  

I think i will struggle running this lot on three amps, i take it my only option is put the supply for the stats through 3amp din rail mounted fuseholders?

i though type D was a bit extreme. It may be because the old pump was a huge belt driven thing.  

i have removed the B6s so was going to change the D16 to a C6 at the disboard.  

The pipe work is 38mm i think with some sections of large welded steel where it would have been impractical due to the number of tee's.  The pump is a grundfos 4180 i have seen a data sheet for it but gave no indiction of loading just pumping stats and so on.  

dont want this to cause problems when firing up, most of the time 3 pumps will start up simultaneously.  

I will take some pics of this lot once done and post them if anyone is interested?